Coupling sleeve for high-pressure pipe

ABSTRACT

A coupling sleeve ( 4 ) for connecting to at least one pipe section ( 2,3 ) fitted in an insertion end ( 29 ) thereof comprises an inner bush ( 5 ) made of thermoplastic material and an outer bush ( 6 ), in which inner bush resistance wires are accommodated, which resistance wires ( 7 ) can be connected to an electric power source for melting the surfaces of the coupling sleeve which face each other and those of each pipe section, in order to create a welded joint, which inner bush and outer bush in axial section have parts ( 8,9 ) which mesh with each other, in order to transmit axial and/or tangential forces. The inner bush has at least one part with a flank which faces the insertion end and which in an axial plane is determined by a tangent forming an angle of less then 45° with the axis of the inner bush.

TECHNICAL FIELD

The invention relates to a coupling sleeve for connecting to at leastone pipe section fitted in an insertion end thereof, which couplingsleeve comprises an inner bush made of thermoplastic material and anouter bush, in which inner bush resistance wires are accommodated, whichresistance wires can be connected to an electric power source formelting the surfaces of the coupling sleeve which face each other andthose of each pipe section, in order to create a welded joint, whichinner bush and outer bush in axial section have parts which mesh witheach other, in order to transmit axial and/or tangential forces.

BACKGROUND OF THE INVENTION

A coupling sleeve of this type for connecting two pipe sections to eachother is known from EP-A-693652. This known coupling sleeve has a numberof concentric casings which are connected to each other by means ofmeshing teeth with a block-shaped cross-section. The object of theseteeth is first of all to provide better heat dissipation during themoulding of the casings in a mould, and said teeth have the additionaladvantage of better mutual adhesion of the casings.

SUMMARY OF THE INVENTION

Pursuant to the invention, it has been recognized that a coupling sleevedesigned in this way is not suitable for use in the case ofhigh-pressure pipes. In such cases the coupling sleeve is exposed tohigh tensile forces. The inner bush of the coupling sleeve welded to theends of two pipe parts is stretched in the process. In view of theuniformity of the forms meshing with each other, the load isconcentrated initially on the outermost forms meshing with each other.This causes a give-way mechanism, in which the forms give way one afterthe other, beginning at the outermost and continuing to the teethsituated further in.

The invention also relates to coupling sleeves which can be fixed to apipe at the insertion end, and which bear, for example, a fixing flangeat the other end.

The object of the invention is to provide a coupling sleeve which isactually suitable for use in the case of high-pressure pipes. Thatobject is achieved by the fact that the inner bush has at least one partwith a flank which faces the insertion end and in an axial plane isdetermined by a tangent forming an angle of less than 45° with the axisof the inner bush.

With such a shape of the meshing forms, a more uniform transmission offorces is obtained, and excessively high tensions in the outermostmeshing forms is avoided, and the meshing forms situated further in canalso participate in the transmission of forces.

The angle between the tangents and the axis is preferably less than 30°.The most preferred angle is one less than 15°.

The coupling sleeve is connected to each of the pipe sections by meansof a continuous circular weld. The transmission of forces between thepipe sections and the coupling sleeve occurs by way of a large weldsurface, with the result that a very gradual pattern of forces occurs inthe axial direction and tension concentrations are avoided.

In particular, the coupling sleeve can comprise an inner bush made ofthermoplastic material and an outer bush, in which inner bush theresistance wires are accommodated.

The desired tensile strength in the direction of both axial ends of thecoupling sleeve can be achieved by the fact that the meshing forms havean asymmetrical cross-section relative to a radial plane. The advantageis that the asymmetry gives the parts greater ability to participate inthe transmission of axial forces.

This asymmetrical shape occurs, for example, in the case of meshingparts comprising teeth which have an asymmetrical cross-section with arelatively steeply slanting tooth flank and a relatively gently slantingtooth flank. The relatively steeply slanting tooth flank of all meshingparts with an asymmetrical cross-section faces away from the insertionend. These teeth do not contribute to the transmission of forces, andthey are therefore kept as short as possible in the axial direction,which results in great steepness. The gradient of the relatively gentlyslanting tooth flank of the meshing forms which are situated at arelatively great distance from the insertion end of the coupling sleeveis smaller than the gradient of the relatively gently slanting toothflank of the meshing parts situated a relatively short distance from theinsertion end, which produces a transmission of forces distributeduniformly over the coupling sleeve.

The size of the gradients of the relatively gently slanting tooth flanksof the meshing forms decreases monotonically in the direction facingaway from the insertion end.

Moreover, the coupling sleeve can be shut off fluently at each end bymeans of conically tapering parts.

The asymmetrical meshing forms according to the invention can bedesigned in various variants.

According to a first variant, the inner bush and the outer bush haveseparate meshing teeth running in the circumferential direction. Suchteeth each form an annular thickening relative to the inner bush and theouter bush.

According to a further variant, the inner bush and the outer bush of thecoupling sleeve have helically meshing tooth systems. Such a helicalshape is suitable for relatively short pipe sections which can bescrewed into the sleeve. The tooth system is asymmetrical, but must alsohave a continuous cross-section, in order to permit the screwingmovement.

The coupling sleeve can be designed in various ways, depending on thepotential applications. If the coupling sleeve can be pushed onto eachpipe section in the axial direction, the coupling sleeve can comprise abush which is in one piece in the circumferential direction, and inwhich the resistance wires are accommodated, running in thecircumferential direction.

In an alternative embodiment, the coupling sleeve can comprise mutuallyconnecting shells, in which the resistance wires are accommodated,running in the axial direction.

The outer bush is fibre-reinforced for bearing axial and/or tangentialforces. The outer bush preferably comprises fibres with a tensilemodulus >50 GPa, such as glass fibres, carbon fibres or aramid fibres.The outer bush also preferably comprises a thermosetting material suchas polyester, vinyl ester or epoxy resin.

The coupling sleeve according to the invention can be used in variousways. First of all, the coupling sleeve is suitable for connecting twopipe sections to each other. In that case the coupling sleeve can besymmetrical relative to a radial plane of symmetry, and the meshingforms on one side of the plane of symmetry are a mirror-symmetricalshape relative to the meshing forms on the other side of the plane ofsymmetry.

According to a variant, the inner bush has two external forms, eachtapering conically towards an axial end, and the outer bush has twocorrespondingly shaped internal forms, which outer bush has anessentially constant thickness.

Coupling sleeves comprising an inner bush with electric resistance wiresare known. Such inner bushes are of standard dimensions and, in view ofthe great forces occurring in high-pressure pipes, could sometimesproduce an inadequate weld. In order to be able to use such standardcomponents in the case of high-pressure pipes in any case, the couplingsleeve can have at least two separate inner bushes situated next to eachother in the axial direction and accommodated in the outer bush.

According to a second variant, the coupling sleeve has one part which isprovided with an insertion end for a pipe section, and also has anauxiliary end to which a further element can be fixed. The auxiliary endcan be provided with a fixing flange, by means of which the couplingsleeve can be connected to, for example, a tank.

The invention also relates to a sleeve joint between two pipe sectionsof a high-pressure pipe, which pipe sections each comprise a fluid-tightinner casing made of a thermoplastic material, and also a reinforcedouter casing, the inner casings being connected to each other in afluid-tight manner, and the outer casings being connected to each otherby means of a coupling sleeve, as described above.

The inner casings are welded to each other directly at their end faceswhich face each other.

The sleeve joint can also be designed in such a way that at the ends ofthe pipe sections facing each other the inner casings are externallyunattached. In that case the coupling sleeve has an inner bush with acentral part of relatively large diameter, which central part of theinner bush is welded to the external surface of the inner casings.

The outer casings can comprise fibres with a modulus >50 GPa, such asglass fibres, carbon fibres or aramid fibres, embedded in athermoplastic matrix.

Furthermore, the outer casings can comprise an outside layer ofthermoplastic material.

The welded joint between the coupling sleeve and the pipe sections isbest achieved if the inner casings and the outer casings and also theinner bush of the coupling sleeve comprise the same thermoplasticmaterial, such as a polyolefin.

A further coupling sleeve is known from WO-A-9512086. This couplingsleeve is particularly suitable for high-pressure pipes, for examplesuitable for pressures up to 100 bar. The joint in the inner casings ofthe pipe sections is obtained by welding, and is consequently suitablefor ensuring the desired tightness. An example which can be mentioned ispipes for transporting gas and crude oil.

In the case of this known sleeve joint, a coupling sleeve is placed onthe ends of the outer casings facing each other. By means of the conicalfixing rings, the coupling sleeve is clamped on the outer surface of theouter casing, the coupling sleeve and the pipe sections being deformedlocally in order to provide the necessary axial retaining power.

This known sleeve joint has various disadvantages. First of all, thelocal deformation of the wall of the pipe sections can give rise totension concentrations, which can lead to giving way, particularly athigh pressures.

A further disadvantage is that several loose components have to be usedfor the joint, which components have to be fitted on the pipe sectionsbeforehand.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail below with referenceto the exemplary embodiments shown in the figures.

FIG. 1 shows the sleeve joint with the coupling sleeve according to theinvention between two pipe sections.

FIG. 2 shows a second variant of the sleeve joint.

FIG. 3 shows the inner bush of the coupling sleeve on a larger scale.

FIG. 3a shows another sleeve joint according to the invention whereinthe inner and the outer bush of the coupling sleeve have a helicallymeshing tooth system.

FIG. 4 shows a third variant of the sleeve joint.

FIG. 5 shows a sleeve joint with flange.

DETAILED DESCRIPTION OF THE INVENTION

The sleeve joint shown in FIG. 1 between two pipe sections 2, 3 of thehigh-pressure pipe comprises a coupling sleeve 4. This coupling sleeveis composed of an inner bush 5 made of thermoplastic material, such as apolyolefin, and an outer bush 6 made of a fibre-reinforced thermosettingcomposite for bearing axial forces. A number of resistance wires 7 areaccommodated on the internal surface of the inner bush 5, whichresistance wires can be connected to a power source by way of connectingterminals (not shown).

The outer surface of the inner bush bears a tooth system 8 running inthe circumferential direction, while the inner surface of the outer bush6 bears a corresponding tooth system 9. These tooth systems 8, 9 meshclosely with each other, in such a way that the loads exerted on theinner bush, particularly those in the axial direction, can betransmitted reliably to the outer bush 6.

The pipes 2, 3 each consist of a fluid-tight inner casing 10 of athermoplastic material, preferably of the same material—such as thepolyolefin—as the inner bush 5 of the coupling sleeve. These innercasings 10 are fixed to each other in a fluid-tight manner at theposition of the weld 11.

The pipes 2, 3 also have an outer casing 12, which is composed of areinforcement fibre layer 13, with, for example, glass fibres, carbonfibres or aramid fibres incorporated in a thermoplastic matrix, and alsoan outer layer of thermoplastic protective material 14.

At the position of the weld 11, the outermost layer 14 of thermoplasticmaterial has been removed, in such a way that the bead 22 formed duringheated plate welding of the fluid-tight inner casings can beaccommodated.

For the formation of the sleeve joint, the thermoplastic material ofboth the inner bush 5 of the coupling sleeve and of the outermost layerof thermoplastic material 14 of the pipe sections 2, 3 is melted, sothat an intimate connection is obtained. After cooling down, the sleevejoint is complete.

The axial tensile forces, which can be considerable in the case ofhigh-pressure pipes, are transmitted by way of the thermoplastic layers14, 5 and the tooth systems 8,9 to the outer bush of fibre-reinforcedmaterial. A reliable and sufficiently strong joint between the pipesections 2, 3 is ensured as a result.

As also shown in FIG. 3, the teeth 8 (and therefore also the teeth 9)have an asymmetrical form. The flanks 23 facing the plane of symmetry 25of the inner bush 5 are steeper than the flanks 24 facing away from saidplane of symmetry 25. Moreover, the steepness of said flanks 24 facingaway from the plane of symmetry 25 increases in the direction towardsthe end of the inner bush 26 (or decreases in the direction of the planeof symmetry 25).

The second variant of the sleeve joint according to the invention, shownin FIG. 2, comprises a coupling sleeve 4 with an outer bush 6 and aninner bush 5, which bushes are connected to each other by tooth system8, 9, corresponding to the variant of FIG. 1.

The inner bush 5 has an inward extending thickened part 28.

Welding wires 7 extend over the entire internal surface of the innerbush 5, in other words, also over said thickened part 28.

The pipe sections 2, 3 each have an inner casing 10 and an outer casing12, likewise corresponding to the variant of FIG. 1.

However, in the case of the variant of FIG. 2, the inner casings 10 arenot welded to each other at their surfaces facing each other. Instead ofthis, the external surfaces of the inner casings 10, which adjoin thethickened part 28 of the inner bush 5 of the welded joint sleeve 4, arewelded to said thickened part. A fluid-tight joint between the innercasings 10 is obtained in this way.

The inner bush 5 is also welded to the outer casing 12. Further workingof the welded joint sleeve 4 shown in FIG. 2 is the same as that of FIG.1.

The alterative embodiment of the sleeve joint shown in FIG. 3a comprisestwo pipe sections 102, 103 and a coupling sleeve 104 having an innerbush 105 and an outer bush 106.

The outer surface of the inner bush 105 and the inner surface of theouter bush 106 bear respective helically meshing tooth systems 108, 109.Such a helical shape is suitable for relatively short pipe sections 102,103 which can be screwed into the sleeve 104. The tooth system isasymmetrical, and has a continuous cross-section, to permit the screwingmovement.

The variant shown in FIG. 4 comprises an inner bush 16 which has twoconical parts 18, 19. Said conical parts 18, 19 fit tightly into thecorrespondingly shaped conical hollows 20, 21 of the outer bush 17.Owing to these shapes, the axial and tangential forces between the innerbush 16 and the outer bush 17 are transmitted in a reliable manner.

In the variant of FIG. 5 the coupling sleeve 4 is hooked by means ofthickening 36 behind the fixing flange 30, which in turn can be fixed bymeans of bolts 31 to, for example, a holder.

The coupling sleeve is pressed against a ring 32, which is sealed bymeans of O-ring 33 relative to the inner casing 10 of pipe section 3,and by means of O-ring 35 can be sealed relative to, for example, anedge around a hole.

The casing 10 is retained by means of bush 34.

What is claimed is:
 1. A coupling sleeve for connecting one pipe sectionto another pipe section, or to an auxiliary part and for forming a pipesection weld between the pipe sections or between the pipe section andthe auxiliary part, the one pipe section having a longitudinal axis andan end portion, the end portion of the pipe section being insertablealong said longitudinal axis into an end of the coupling sleeve, thecoupling sleeve comprising: (a) an inner bush comprising thermoplasticmaterial and having an inner surface to contact the pipe section and anouter surface; (b) an outer bush having an inner surface and an outersurface, the outer bush inner surface and the inner bush outer surfacehaving mutually engaging teeth to transmit loads from the inner bush tothe outer bush wherein, in axial cross section, each inner bush tooth ispointed and points away from the pipe section longitudinal axis with aflank on one side of the tooth point being oriented to face the pipesection end and slanting relatively steeply with respect to the pipesection longitudinal axis and a flank on the other side of the toothpoint oriented to face away from the pipe section end and slantingrelatively gently with respect to the pipe section longitudinal axis;and (c) at least one resistance wire accommodated by the inner surfaceof the inner bush, wherein the resistance wire can be connected to anelectric power source to provide heat to melt the thermoplastic materialand to form the pipe section end.
 2. A coupling sleeve as claimed inclaim 1, wherein the relatively gently slanting flanks slant at an angleof less than 33°, optionally less than 15°, with respect to the innerbush longitudinal axis.
 3. A coupling sleeve as claimed in claim 1,wherein the inner bush teeth are symmetrically disposed on either sideof the joint location whereby the relatively steeply slanting flanks ofthe teeth on one side of the joint location face the relatively steeplyslanting flanks on the other side of the joint location.
 4. A couplingsleeve as claimed in claim 1, wherein the relatively steeply slantingteeth flanks of the inner bush face away from the insertion end of thecoupling sleeve.
 5. A coupling sleeve as claimed in claim 1, wherein thegradient of each relatively gently slanting tooth flank of the innerbush situated at a relatively lesser distance from the insertion end issmaller than the gradient of a relatively gently slanting tooth flank ofthe inner bush situated at a relatively greater distance from theinsertion end.
 6. A coupling sleeve as claimed in claim 5, furthercomprising a plane of symmetry perpendicular to a longitudinal axis ofthe coupling sleeve, optionally at a center point of the longitudinalaxis of the coupling sleeve, wherein the angles of the gradients of therelatively gently slanting tooth flanks decrease, optionally linearly,in the direction along the longitudinal axis toward the plane ofsymmetry.
 7. A coupling sleeve as claimed in claim 1, wherein the innerbush tapers conically toward the inner bush ends.
 8. A coupling sleeveas claimed in claim 1, wherein the inner bush and the outer bush havemultiple separate mating teeth each said tooth having a continuouscircumferential extent.
 9. A coupling sleeve as claimed in claim 1,wherein the inner bush and outer bush have helically mating teeth.
 10. Acoupling sleeve as claimed in claim 1, wherein the outer bush isfiber-reinforced for bearing axial or tangential forces, or axial andtangential forces.
 11. A coupling sleeve as claimed in claim 10, whereinthe outer bush comprises fibers with a tensile modulus greater than 50Gpa, optionally glass fibers, carbon fibers or aramid fibers.
 12. Acoupling sleeve as claimed in claim 1, wherein the outer bush comprisesa thermosetting material optionally a polyester, a vinyl ester or anepoxy resin.
 13. A coupling sleeve as claimed in claim 1, wherein theinner bush is in one piece in the circumferential direction, and theresistance wires are disposed on the inner surface of the inner bush andrun in the circumferential direction.
 14. A coupling sleeve as claimedin claim 1, wherein the inner bush comprises mutually connecting shellsand the resistance wires run in the axial direction.
 15. A couplingsleeve as claimed in claim 1, wherein the coupling sleeve is in onepiece having an insertion end for the pipe section, and an auxiliary endfor fixing the auxiliary part.
 16. A coupling sleeve as claimed in claim15, wherein the auxiliary end is fixed to a fixing flange.
 17. Acoupling sleeve as claimed in claim 15, wherein the inner bush comprisesat least two separate inner bush sections situated next to each other inthe axial direction and accommodated in the outer bush.
 18. A sleevejoint between two pipe sections of a high-pressure pipe, wherein thepipe sections each comprise a fluid-tight inner casing made of athermoplastic material, a reinforced outer casing and an end of the pipesections, the pipe section ends facing each other, the inner casingsbeing connected to each other in a fluid-tight manner and the outercasings being connected to each other by means of a coupling sleeve asclaimed in claim
 1. 19. A sleeve joint as claimed in claim 18, whereinthe inner casing end faces are directly welded to each other.
 20. Asleeve joint as claimed in claim 18, wherein at the ends of the pipesections the inner casings have free external surfaces and the couplingsleeve has an inner bush with a central part of relatively largediameter, the central part of the inner bush being welded to theexternal surface of the inner casings.
 21. A sleeve joint as claimed inclaim 18 wherein the outer casings comprise fibers with a modulusgreater than 50 GPa, optionally glass fibers, carbon fibers or aramidfibers, embedded in a thermoplastic material.
 22. A sleeve joint asclaimed in claim 18, wherein the inner casings and the outer casings andalso the inner bush of the coupling sleeve comprise the samethermoplastic material, optionally a polyolefin.
 23. A sleeve joint asclaimed in claim 21, wherein the outer casings comprise an outermostlayer of thermoplastic material optionally, a polyolefin.
 24. A couplingsleeve for connecting one pipe section to another pipe section, or to anauxiliary part, and for forming a pipe section weld between the pipesections or between the pipe section and the auxiliary part, the onepipe section having a longitudinal axis and an end portion, the endportion of the pipe section being insertable along said longitudinalaxis into the coupling sleeve, the coupling sleeve being symmetrical oneither side of a radial plane of symmetry perpendicular to the pipesection longitudinal axis and comprising: (a) an inner bush comprisingthermoplastic material and having an inner surface to contact the pipesection and an outer surface; (b) an outer bush having an inner surfaceand an outer surface, the outer bush inner surface conforming with theinner bush outer surface along the length of at least one of the sleevesand around the inner bush outer surface; and (c) at least one resistancewire accommodated by the inner surface of the inner bush, wherein theresistance wire can be connected to an electric power source to provideheat to melt the thermoplastic material and to for the pipe section;wherein the resistance wire has an extent along the coupling sleeve andthe inner bush outer surface tapers away from the plane of symmetrythroughout the longitudinal extent of the resistance wire.
 25. Acoupling sleeve as claimed in claim 24, wherein the inner bush comprisesat least two separate inner bush sections situated next to each other inthe axial direction and accommodated in the outer bush.
 26. A couplingsleeve as claimed in claim 24, wherein the outer bush has a constantthickness along its longitudinal axis.
 27. A coupling sleeve as claimedin claim 24, wherein the outer bush surface is convexly curved in boththe circumferential and longitudinal directions.
 28. A coupling sleeveas claimed in claim 24, wherein the resistance wire and the inner andouter bushes have the same longitudinal extent.
 29. A sleeve jointbetween two pipe sections of a high-pressure pipe, wherein the pipesections each comprise a fluid-tight inner casing made of athermoplastic material, a reinforced outer casing and a pipe sectionend, the pipe section ends facing each other, the inner casings beingconnected to each other in a fluid-tight manner and the outer casingsbeing connected to each other by means of a coupling sleeve as claimedin claim
 24. 30. A sleeve joint as claimed in claim 29, wherein theinner casings are welded to each other directly at their end faces,wherein the end faces face each other, the inner casings having freeexternal surfaces and the coupling sleeve has an inner bush with acentral part of relatively large diameter, the central part of the innerbush being welded to the external surface of the inner casings, theouter casings comprise fibers with a modulus >50 GPa, optionally glassfibers, carbon fibers or aramid fibers, embedded in a thermoplasticmaterial and an outermost layer of thermoplastic material, optionally, apolyolefin.
 31. A coupling sleeve for connecting at least one pipesection to another pipe section, or an auxiliary part, to create a pipesection weld between the pipe sections or the pipe section and theauxiliary part, the pipe section having a longitudinal axis and an endportion of the pipe section being inserted along the longitudinal axisinto the coupling sleeve, the coupling sleeve comprising: (a) an innerbush comprising thermoplastic material and having an inner surfacecontacting the pipe section and an outer surface comprising at least oneflank, each flank rising radially outwardly toward a joint at a riseangle of less 45°, the rise angle being defined by the interaction of atangent to the flank with the pipe section longitudinal axis; (b) anouter bush comprising an inner surface and an outer surface, the innersurface comprising multiple flanks, the flanks having an angular axialcross-section capable of mating with the at least one flank of the innerbush wherein the mating flanks are comprised by teeth, each tooth havinga relatively steeply slanting flank and a relatively gently slantingflank on the opposed side of a radial plane through the respectivetooth, the radial plane being perpendicular to the longitudinal axis ofthe pipe; and (c) at least one resistance wire disposed between theinner bush and the pipe section, wherein the resistance wire can beelectrically powered to provide heat for melting adjoining surfaces ofthe inner bush and the pipe section, the melted sections forming a pipesection end t o transmit axial or tangential forces, or transmit axialand tangential forces from the inner bush to the outer bush.